The broad aim of this study is to increase our understanding of the local flow processes which take place in the blood microcirculatory system (and its environs), and to relate the behavior of such flows to the macroscopic rheological properties of blood. Experimental data are being obtained from experiments in which flows through long, single, artificial tubes whose inside diameters range from 4 microns up to several hundred microns. Among the variables measured are tube dimensions; blood rheological properties; hematocrits in the feed reservoir, tube and outflowing blood; blood and red cell velocities; and pressure drops. Mathematical models of these flows are being tested. This work is being extended to studies of pulsatile flow in single tubes, bifurcations, and in replicas of real microcirculatory networks. The red cell deformability and aggregability are to be altered. The effects of these alterations on blood's rheological properties and on local blood flow characteristics in the flow geometries mentioned above will be assessed.